Television signal-translating system



W. F. BARES TELEVISION SIGNAL-TRANSLATING SYSTEM Juiy 3o, 1946.

Filed. Feb. 27', 1942 Patented Julyv 30, 1946 TELEVISION SIGNAL-TRANSLATING SYSTEM William F. Bailey, Port Washington, N. Y., assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, Ill., a corporation of Illinois Application February 27, 1942, Serial No. 432,669

8 Claims.

This invention relates to a television signaltranslating system and, more particularly, to a video-frequency signal-translating system having an improved characteristic effective in compensating for shading effects in the reproduced picture.

In video-frequency signal-generating systems, especially those in which a camera tube having a target electrode comprising a mosaic plate is em- Dloyed as the video-frequency signal generator, there is produced, in addition to the desired video-frequency signals corresponding to the image to be translated, an undesired, spurious signal, commonly known as a shading signal. This undesired signal is produced, at least in part, by secondary electrons emitted from the target electrode during the scanning operation. The emitted secondary electrons rain back upon the target electrode but, in general, this rain is not uniform over the area of the target so that the several elements of the target do not assume potentials accurately representative of their respective degrees of illumination, Consequently, the output signal of the cameraV tube includes an undesired component resulting in a shading effect in the reproduced picture. Since the shading effect is produced in part by the scanning operation, the shading signal contains frequency components related to the scanning frequencies of the system. The amplitude of the undesired signal under consideration is generally of a greater order of magnitude than that of the desired video-frequency signal so that it is necessary to delete from the composite output signal of the camera tube those components which correspond to the undesired shading signal if high-quality image translation is to be attained.

For the purpose of minimizing shading effect of the type under consideration, it has been proposed in the past to include a collector ring in the camera tube having a circular shape symmetrical with respect to the mosaic and particularly adapted for collecting the secondary electrons. It has also been proposed to use small values of beam current in the camera tube to reduce the shading effect. Another expedient resorted to for the same purpose is to avoid scanning the edges of the mosaic Where the variations in the rain of electrons back to the mosaic are the greatest. However, systems in which these DIOIJOSES have been utilized are subject to the disadvantage that a substantial shading effect remains and that the amplitude of the undesired shading signal produced is generally greater than that of the de- 2 sired video-frequency signals, in spite of the aforementioned expedients.

As a still further expedient, it has been proposed to minimize the shading component in the output signal of a camera tube by utilizing a suitable, artical compensating signal which may be inserted in the video amplifier. It has been found that such an artificial signal having a saw-tooth, exponential or parabolic Wave form may in some cases be effective to reduce, to a limited extent, the undesired shading effect. In some instances the compensating signal is a composite signal comprising a combination of these Wave forms, and having frequency components related to the scanning frequencies of the signal generator. This method of compensating has the disadvantage that it requires elaborate and extensive equipment which is both difficult and inconvenient to operate successfully.

It is an object of the present invention, therefore, to provide an improved television signaltranslating system Which is not subject to one or more of the above-mentioned disadvantages.

It is still another object of vthe invention to provide a television signal-translating system having an improved arrangement for removing, at least in Dart, from the signal translated thereby an undesirable component introduced into the signal in the signal generator and normally eiective to produce a shading effect in the reproduced picture.

It is a still further object of the invention to provide an improved method and means for translating television signals substantially free from components related to the scanning frequencies of the translating system and normally effective to produce a shading effect in the reproduced picture.

A specific object of this invention is to provide in a television signal-translating system an automatic means for shading correction which means does not require the services of an operator regardless of the shading wave form.

In accordance with the invention, a television signal-translating system includes a signaltranslating channel having an input circuit and an output circuit, and means for applying to the input circuit a composite signal derived by scanning continuous lines of an image to be translated which signal comprises video-signal components Within a predetermined frequency range corresponding to images to be translated in the system and undesirable shading components having frequencies within this range and related to a frequency of scanning of the image. |Also included in the system are means having a frequency characteristic related to the above-mentioned scanning frequency for effectively removing from the compo-site signal at least one lower frequency component of the shading components and for translating to the output circuit the resultant signal which includes video-signal components having frequencies below the above-mentioned lower frequency component and is substantially free from each removed shading component.

In accordance with a preferred embodiment of the invention, a repeater circuit including a plurality of trap circuits is coupled in the signaltranslating channel. rIhe trap circuits, which may be either series or parallel arrangements of inductors and capacitances, are resonant at the fundamental and at least one harmonic of the line-scanning frequency and are effective to remove from the translated signal components of those frequencies which correspond to shading components. A coupling circuit, which comprises a stabilizing device coupled to the repeater circuit, is provided and is effective to suppress shading components related to the held-scanning frequency. To this end, the coupling circuit has a time constant which is short with respect to the field-scanning frequency and rejects components of the translated signal at that frequency.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope Will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a circuit diagram, partly schematic, of a television transmitting system including a circuit arrangement embodying the present invention; Fig. 2 is a circuit diagram of a modification of the arrangement of Fig. 1; Fig. 3 comp-rises a graph representing certain operating characteristics of the circuit of Fig. 2; and Fig. 4 is a circuit diagram of a further modification of the arrangement of Fig. 1.

Referring now more particularly to Fig. l of the drawing, there is illustrated a television transmitting system comprising a signal generator Ii), which may be of conventional design including a camera tube of the cathode-ray type, having a mosaic type target electrode and scanning elements Il and I2. developing scanning currents for the signal generator III there are provided a line-frequency saw-tooth wave generator I3 and a field-frequency saw-tooth wave generator M, the output circuits of these generators being connected to scanning elements II and I2, respectively, of the signal generator IB in the usual manner. In order to block out the scanning ray of the generator lil during retrace scanning periods, there is provided a block-out wave generator I5 having an output circuit suitably connected to the signal generator I0.

For the purpose of synchronizing the generators there is provided a timing-impulse generator I5 coupled to the input circuits of the generators I3-I5, inclusive. Timing-impulse generator I6 is preferably stabilized by means of a connection i'l to a suitable source of periodic voltage, for example, the power-supply circuit or the synchronizing-voltage source of a motion-picture mechanism where such is employed.

Connected in cascade to the generator I il, in the order named, are a signal-translating stage 2S, a video-frequency amplifier 2|, a modulator 22, an associated carrier-frequency oscillator 23,

For the purpose of i a power amplifier 24, and an antenna system 25, 2G all, with the exception of the translating stage 2li which embodies the present invention as will be described more fully hereinafter, are constructed and arranged in accordance with conventional practice. Line-synchronizing pulses and held-synchronizing pulses are derived from line-frequency generator I3 and field-frequency generator lli, respectively, and supplied to the video-frequency amplifier 2l for translation with the video-frequency signals generated in unit I0. Suitable means (not shown, but which may be considered as included in the signal generator l0) are also provided for developing a unidirectional background-illumination voltage and for inserting it into the developed video-frequency signal.

Neglecting for the moment details of operation of the signal-translating stage 26, the system just described comprises the elements of a television transmitter of conventional design and the various parts thereof, which are illustrated schematically, may be of well-known construction, rendering a detailed description of their operation unnecessary. Brieiiy, however, the image of a scene to be transmitted is focused on the target of the signal generator I0 and scanning currents are applied to the scanning elements Il and I2 of the generator l0 to supply electro-magnetic fields which serve to deflect the scanning ray in two directions normal to each other, thereby to scan successively a series of elds of parallel lines upon the target. The delecting currents, and hence the scanning fields, are of sawtooth wave form providing relatively slow linear trace and rapid retrace scansions. Block-out impulses developed by generator I5 are applied to the signal generator I to suppress or block out the scanning beam during retrace portions of the scanning cycles. The timing impulses developed by the generator I6 are applied to generators I3- |5, inclusive, to lock these generators in synchronism.

The photosensitive elements of the target of the signal generator IEI are electrically affected to an extent dependent upon the varying values of light at the corresponding elemental areas of the image focused thereon so that, as the cathode-ray beam scans continuous image lines of the image on the target, Video-frequency signals of correspondingly varying amplitude, and having a frequency range determined by the images to be translated, are developed in the generator I0. The terms video signal or video-frequency signal, as employed in the specification and claims, are intended to designate a conventional picture signal which is generated by the usual scanning operation. This terminology therefore excludes a generated picture signal, the wave form of which is modified by interrupting the scanning beam by suitable means at a high frequency so that the picture signal, in effect, modulates the developed interrupting wave, this latter wave being in the nature of a carrier wave. The interruption of the scanning beam in the foregoing manner therefore effectively prevents the beam from scanning continuous image lines of the image to be translated as in customary scanning practice. At the same time as the conventional video-frequency signals are generated, due to the above-mentioned secondary-electron effect, shading signals having components related to the line-scanning frequency and field-scanning frequency and included within the frequency range of the video-frequency signals are also developed in the generator Ill. These developed signals comprise a composite signal derived by the generator I0 and the unidirectional background-illumination voltage which is developed by suitable means included in the generator IG is inserted in this signal. Thus, the video-frequency and shading-signal components, blockout components, and unidirectional-background components are all derived from the signal generator I0 and applied to the signal-translating stage 29, wherein they are translated in accordance with the present invention and from which they are applied to the video-frequency amplifier 2|. synchronizing impulses derived from generators I3 and i4 are mixed With the videosignal components in the combining video-frequency amplifier 2| and the resultant signal is thereupon supplied to the modulator 22 wherein it is impressed upon the carrier wave generated by the oscillator 23. The modulated carrier signal is then delivered to the power amplifier 2d. for amplification and is impressed upon the antenna system 25, 2'5 to be radiated.

Referring now more particularly to the signaltranslating stage 2Q embodying the :resent invention and provided for the purpose of removing shading components from the composite signal to be translated, this stage comprises a pair of vacuum tubes 21 and 23, which are preferably of the pentode type, coupled in cascade to provide a signal-translating channel having an input circuit connected to signal generator Hi and an output circuit connected to video-frequency amplifier 2|.

The input circuit of the signal-translating channel includes the signal-input electrode of tube 21 and is coupled to the output circuit of signal generator by way of a coupling condenser 29 and a grid-leak resistor 3d. Tube 21, which functions as a signal repeater, is provided with means having a frequency character'- istic related to one scanning frequency of the signal generator lll to render the tube degenerative to applied signal components of predetermined frequencies for attenuating from the composite signal applied thereto components having a frequency related to the saine scanning frequency and corresponding to shading components in the signal output of generator it. Specifically, there is provided in the cathode circuit of repeater 21 a pair of parallel-resonant trap circuits connected in series. The rst trap circuit comprises a parallel combination of an inductor 3|, a condenser 32, and a damping resistor 33, and this trap circuit is tuned preferably to the fundamental frequency of the linefrequency generator |3. The second trap circuit comprises the parallel combination of an inductor 34, a condenser 35, and a resistor 36, and this trap circuit is tuned preferably to the second harmonic of the line-scanning frequency. The damping resistors 33 and 3S are provided in order to broaden the attenuation characteristics of the trap circuits. The output circuit of tube 21 is provided with a load resistor 31 and is coupled to the input circuit of tube 23 through a time-constant circuit which comprises coupling condenser 39 and grid-leak resistor 40. The time constant of the circuit coupling tubes 21 and 28 is proportioned with respect to another scanning frequency of the generator lll and, preferably, the circuit is arranged to have a time constant short with respect to the period of the eldfrequency generator I4 so that the coupling circuit has a frequency characteristic related to the field-scanning frequency. The output cirlll '. the shading signal.

cuit of the signal-translating stage includes a load resistor 4| and is suitably coupled to the input terminals of video-frequency amplier 2|. Operating potentials for tubes 21 and 28 are supplied to their screens from suitable sources indicated -l-Sc and to their anodes from suitable sources indicated -l-B.

In considering the operation of the circuit of Fig. 1, it will be assumed that composite signals comprising video-signal components Within a predetermined frequency range corresponding to the images to be translated and undesired shading components having frequencies within the range and related to the line-scanning and fieldscanning frequencies of the signal generator l0 are applied negatively, that is, with the black level of the composite signal more negative than the white level thereof, by way of coupling condenser 29 to the input circuit of the signal-translating channel and to tube 21, The time constant of condenser 2S and grid-leak resistor 3G is such that the signal is not stabilized about its positive peaks in the input circuit of tube 21. The trap circuits included in the cathode circuit of tube 21 are effective to render the tube degenerative to applied signal components of the fundamental frequency and the second harmonic, respectively, of the line-scanning generator whereby components of the composite signal at these frequencies, which correspond to components of the undesired shading signal, are effectively removed and do not appear in the repeated signal which is derived from the output circuit of tube 21. Due to the phase-reversing characteristic of tube 21, the repeated signal is applied positively, that is, with the black level of the signal more positive than the white level thereof, by way of coupling condenser 3i) to tube 28 wherein the signal is stabilized through grid rectification at the most positive peaks of the signal. The time-constant circuit comprising condenser 39 and leak resistor 4l! is effective to remove from the signal applied to tube 28 components at the eld-scanning frequency which also correspond to components of Thus, a composite signal from which the undesirable shading components have been removed is derived from the output circuit of the signal-translating channel 2|) and applied to video-frequency amplifier 2| for further amplification.

Therefore, it may be seen that the unit 20 is effective to remove undesired shading components from a composite signal comprising both desired video-signal components and undesired shading components within the frequency range of the video-signal components and related to a frequency at which the image to be translated is scanned, whereby the video-signal components supplied to amplifier 2| are thus substantially free from shading components caused by the scanning operation at the signal generator.

In Fig. 2 there is disclosed a repeating network embodying a modification of the invention which may be substituted in the television transmitting system of Fig. 1 for the signal-translating stage 20 by connecting the terminals indicated C and D to the corresponding terminals of Fig. l. The network includes a pair of vacuum-tube repeaters 50 and 5| which preferably are of the pentode type. The input electrode of tube '50 is coupled through a coupling condenser E2 and a grid-leak resistor 53 to the output circuit of generator I0 and the signal output from tube 50 is derived from a cathode load resistor 54 so that the output signal has the same polarity as the input signal. The input circuit of tube 5| is coupled in parallel with that of tube 50 and includes a coupling condenser E5 and a leak resistor 5l. Also included in the input circuit of tube 5l is a low-pass filter network comprising series resistors E8 and SQ and shunt condensers 59 and (il. The output signal of tube 5l is derived from an anode load resistor 62 and, due to the phase-reversing characteristic of the tube, the signal derived therefrom has a polarity opposite to that of the signal-input thereto. A condenser 63 is connected between the anode of tube 5l and the cathode of tube 53 whereby the tubes are connected in phase opposition.

Tube 50 has a substantially uniform gain characteristic over the frequency range of the videosignal components while the filter 58 to @l causes the tube 5I to have a gain characteristic related to a frequency at which the image to be translated is scanned. Specifically, the low-pass nlter 58 to 6| is arranged to reject frequency components of the applied signal which are of a frequencsr equal to or greater than the third harmonic of line-frequency generator i3. The coupling circuit associating the output circuits of the repeater tubes 5t and lil has a frequency characteristic related to another lfrequency at which the image to be translated is scanned and, specifically, the coupling circuit is arranged to have a time constant which is short with respect to the frequency of the field-scanning generator I4.

In considering the operation of the circuit of Fig. 2, it will be seen that the composite signal, defined above, is derived from signal generator l and applied to tube 59 and that a signal of the same polarity is developed across its cathode load e. The signal output of generator 0 is also applied to the input circuit of tube 5I, but the components of the signal having a frequency equal to or greater than the third harmonic of the line-scanning frequency are rejected by the low-pass filter 5B to Si and, therefore, do not appear in the output circuit of tube 5i. Signal components of the lower frequencies, however, are translated in repeater 5l to substantially the same extent that these components are translated in repeater The signal output of tube 5| developed across the anode resistor 62 is of opposite polarity to that developed across cathode resistor 54 of the tube 50 so that these outputs when coupled together through condenser S3 tend to cancel one another for the frequencies under consideration. Due to the above-defined time constant of the coupling circuit, however, coupling condenser 63 is effective to block components of the repeated signal of tube 5| of a frequency less than the fundamental of the linescanning frequency and, since only components of the applied signal having frequencies up to the third harmonic of the line-scanning frequency appear in the output circuit of the tube 5l, a band of frequencies extending substantially from the fundamental to the third harmonic of the line-scanning frequency is effectively suppressed in the output circuit of tubes 5l) and 5l The output characteristic of the repeating network is represented in Fig. 3 wherein f1, f2, and f3 indicate the fundamental, second, and third harmonics, respectively, of 'the line-scanning frequency.

Consequently, it may be seen that the repeating network of Fig. 2 is effective to remove from the composite signal applied thereto or appreciably to attenuate a band of frequencies including the fundamental, second, and third harmonics of the line-scanning frequency which correspond to shading components which are particularly troublesome, whereby the video-signal components of the composite signal are translated to the output circuit of the signal-translating channel substantially free from shading components of frequencies related to the line-scanning frequency.

In the modification of the invention disclosed in Fig. 4, the means provided for attenuating shading components comprises a pair of shuntconnected series-resonant trap circuits coupled in the signal-translating channel, The rst trap circuit includes an inductor "55? and condenser 'li and is tuned, preferably, to the fundamental of the line-scanning frequency, while the second trap circuit includes inductor 'i2 and condenser 'i3 tuned, preferably, to the second harmonic of the line-scanning frequency. The circuit of Fig. 4 may be substituted for the signal-translating stage 2e in Fig. `l by connecting terminals C and i) to the correspondingly designated terminals of Fig. l. When this substitution has been effected the composite signal applied to terminal C is translated and applied to video-frequency amplifier El, but components of the signal having frequencies corresponding to the first and second harmonics of the line-scanning frequency and ccrresponding to shading components are attenuated by the trap circuits.

It is appreciated that in utilizing the principles and concepts of the invention, certain desired picture components may be removed from the translated signal; that is, in attenuating frequency components related to the undesired shading signals components of the desired video signals of the same frequency are simultaneously attenuated. However, the deletion of such small portions of the relatively wide frequency band representative of the video signals to be translated does not appreciably affect the picture content of the signal, That is, the frequency components which are removed are of relatively low frequencies which control the shade of the picture rather than the picture details and, hence, the sharpness of the reproduced picture is not adversely affected. At the same time, removal of the shading components, particularly those related to the line-scanning frequency which are most pronounced, enables the reproduction of a translated image which is sufficiently improved over the reproduction of images wherein the shading components have not been removed to more than compensate the inherent loss of naturalness in the reproduction caused by the deletion of a portion of the video signals.

There has been included in the above-described embodiments of the invention means for removing from the composite signal frequency components corresponding to the fundamental, second, and third harmonics of the line-scanning frequency, as well as components corresponding to the fundamental and one or more harmonics of the field-scanning frequency. It is, of course, to be understood that any desired combination of frequency components related to scanning frequencies and corresponding to an undesired shading signal may be similarly removed by rearranging or increasing the number of the trap circuits employed. The specific embodiments disclosed are merely illustrative of some possible combinations.

Although the invention has been disclosed in connection with a television transmission system,

9 it is to be further understood that the principles and embodiments of the invention may be applied With equal facility to a television receiving system to accomplish the purposes accomplished by the invention when applied to a television transmission system.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A television signal-translating system comprising, a signal-translating channel having an input circuit and an output circuit, means for applying t said input circuit a composite signal derived by scanning continuous image lines of an image to be translated and comprising vvideosignal components within a predetermined frequency range corresponding to images to be translated in said system and undesirable shading components having frequencies within said range and related to a frequency of scanning of said image, and means in said channel having a frequency characteristic also related to said scanning frequency for effectively removing from said composite signal at least one lower frequency component of said shading components and for translating to said output circuit the resultant signal Which includes video-signal components having frequencies below said lower frequency component and is substantially free from each said removed shading component.

2. A television signal-translating system comprising, a signal-translating channel having an input circuit and an output circuit, means for applying to said input circuit a composite signal derived by scanning an image to be translated and comprising video-signal components within a predetermined frequency range corresponding to images to be translated in said system and undesirable shading components having a frequency within said range and related to a frequency of scanning of said image, a trap circuit in said channel resonant at said frequency within said range for attenuating frequency components corresponding to said shading components, and means in said channel for translating to said output circuit the resultant signal including video-signal components having a frequency below the fundamental frequency of said scanning frequency and substantially free from said shading components.

3. A television signal-translating system comprising, a signal-translating channel having an input circuit and an output circuit, means for applying to said input circuit a composite signal derived by scanning an image to be translated and comprising video-signal components within a predetermined frequency range corresponding to images to be translated in said system and undesirable shading components having a frequency within said range and related to a frequency of scanning of said image, and a seriesresonant trap circuit connected in shunt to said channel and resonant at said frequency within said range for attenuating frequency components corresponding to said shading components, said channel being adapted to translate to said output circuit the resultant signal substantially free from shading components.

4. A television signal-translating system comprising, a signal-translating channel having an input circuit and an output circuit, means for applying to said input circuit a composite signal derived by scanning an image to be translated and comprising video-signal components within a predetermined frequency range corresponding to images to be translated in said system and undesirable shading components having a frequency within said range and related to a frequency of scanning of said image, a repeater circuit in said channel, and a trap circuit included in said repeater circuit and resonant at said frequency within said range for attenuating frequency components corresponding to said shading components, said repeater circuit being adapted to translate to said output circuit the resultant signal including video-signal components having a frequency below the fundamental frequency of said scanning frequency and substantially free from said shading components.

5. A television signal-translating system comprising, a signal-translating channel having an input circuit and an output circuit, means for applying to said input circuit a composite signal derived by scanning an image t0 be translated and comprising video-signal components within a predetermined frequency range corresponding to images to be translated in said system and undesirable shading components having a frequency within said range and related to a frequency of scanning of said image, a repeater circuit in said channel comprising a vacuumtube repeater having a cathode circuit, a parallel-resonant trap circuit included in said cathode circuit and resonant at said frequency within said range for attenuating frequency components corresponding to said shading components, said repeater circuit being adapted to translate to said output circuit the resultant signal substantially free from said shading components.

6. A television signal-translating system oomprising, a signal-translating channel having an input circuit and an output circuit, means for applying to said input circuit a composite signal derived by scanning continuous image lines of an image to be translated and comprising video-signal components within a predetermined frequency range corresponding to images to be translated in said system and undesirable shading components having a frequency within said range and related to a frequency of scanning of said image, a repeater network in said channel, a pair of repeaters in said network adapted to produce output signals of opposite polarity, one of said repeaters having a substantially uniform gain characteristic over the frequency range of said video-signal components and the other of said repeaters having a gain characteristic over said range related to said scanning frequency, output circuits for said repeaters, and means for coupling said output circuits so that frequency components of said composite signal corresponding to said shading components are removed in said repeater network, said repeater network being adapted to translate to said output circuit of said channel the resultant signal substantially free from said shading components.

7. A television signal-translating system comprising, a signal-translating channel having an input circuit and an output circuit, means for applying to said input circuit a composite signal derived by scanning continuous image lines of an image to be translated at a plurality of scanning frequencies and comprising video-signal lll components within a predetermined frequency range corresponding to images to he translated in said system and undesirable shading components having frequencies in a given band within said range and related to one of said scanning frequencies, a repeater network in said channel, a pair of repeaters in said network adapted to produce output signals of opposite polarity, one of said repeaters having a substantially uniform gain characteristic over the frequency range of said video-signal components and the other of said repeaters having a gain characteristic over said range related to one of said scanning frequencies, output circuits for said repeaters, and a coupling circuit having a time constant short with respect to the period cf another of said scanning frequencies for cennecting said output circuits of said repeaters so that frequency components within said band of frequencies are effectively removed from said composite signal, said repeater network being adapted to translate to said output circuit cf said channel the resultant signal substantially free from said shading components.

8. A television signal-translating system cornprising, a signal-translating channel having an input circuit and an output circuit, means for applying to said input circuit a composite signal derived by scanning continuous image lines 12 of an image to be translated, said scanning being effected in one direction at a predetermined line-scanning frequency and in another direction normal to said mst-mentioned direction at a predetermined field-scanning frequency and said composite signal comprising video-signal components within a predetermined frequency range corresponding to images to be translated in said system and undesirable shading components having frequencies within said range and related to said line-scanning and said eldscanning frequencies, means in said channel having a frequency characteristic related to said line-scanning frequency for effectively removing from said composite signal shading-signal frequency components related to said line-scanning frequency, and means in said channel having a frequency characteristic related to said fieldscanning frequency for effectively removing from said composite signal shading-signal frequency components related to said field-scanning irequency and for translating to said output circuit the resultant signal including video-signal components having a frequency below the fundamental frequency of said line-scanning frequency and above the fundamental frequency of said held-scanning frequency and substantially free from said shading components,

WILLIAM F. BAILEY. 

